The growth of spherulites of poly(ethylene oxide) in blends with poly(hydroxyether of bisphenol A) was investigated. In a very narrow range of crystallization temperatures, the spherulite growth deviates from the usual constant growth rate regime in a systematic manner in which the growth rate decreases with time. This is explained by local and overall changes in the composition with the proceeding crystallization that are due to the competition between the crystallization and diffusional chain displacement rates? respectively. These kinetic phenomena and processes can quantitatively be described by a suitable analysis of the experimental findings. Deceleration is predominantly caused by a slowing of the chain motion by the glass-transition temperature being approached (i.e., vitrification) and, to a lesser extent, by dilution.